Diversity, evolution, form-structure-function relationships and biomimetic potential of plant hinges

Scientist: Arooj Sajjad

Plant movements are often enabled by joint-like structures, commonly named “plant hinges”. A very popular and well-investigated example for such a hinge is the pulvinus, which allows the sensitive Mimosa to fold its leaves upon touch (Fig. 1). Unlike technical hinges, which rely on rigid body movements that are maintenance-intensive and prone to failure, motile plant structures employ functionally robust compliant mechanisms.

In this project, plant hinges are comparatively analyzed from evolutionary, functional, structural, and biomechanical perspectives. The goal is to systematically and comprehensively study different types of hinges in the plant kingdom and compile them into a ‘phylogeny of plant hinges’ and eventually into a hinge catalogue for application-oriented purposes.

Figure 1: The sensitive Mimosa (Mimosa pudica) folds its leaflets and whole leaves upon touch. The movements are enabled by elastically deformable miniature hinges, i.e. the pulvini, at the bases of these structures.
Figure 1: The sensitive Mimosa (Mimosa pudica) folds its leaflets and whole leaves upon touch. The movements are enabled by elastically deformable miniature hinges, i.e. the pulvini, at the bases of these structures.

Below you can see two examples out of the very high diversity of plant hinges. Firstly, the orchid Bulbophyllum echinolabium has a movable flower lip for interaction with pollinating insects (Fig. 2). The movement is driven by the forces applied by the pollinator, e.g. a fly, and is always uniaxial.

Figure 2: The flower lip of the orchid Bulbophyllum echiolabium shows uniaxial movement upon application of external mechanical force, e.g. by a fly.
Figure 2: The flower lip of the orchid Bulbophyllum echiolabium shows uniaxial movement upon application of external mechanical force, e.g. by a fly.

The second example shows the obedient plant (Physostegia virginiana), whose hinged flowers can be bent or rotated into all possible positions by external forces acting on them (Fig. 3). The various structures involved and the kinematics implemented are largely unexplored, although they (could) have a very high biomimetic potential.

The flowers of the obedient plant (Physostegia virginiana) can be bent and rotated in various positions.
The flowers of the obedient plant (Physostegia virginiana) can be bent and rotated in various positions.